Flat heat transfer tube

ABSTRACT

A flat heat transfer tube has upper and lower walls and fluid channels. Two to five inner fins are formed on each of two surfaces of the flat walls facing each fluid channel. The tube height is 1.8 mm or less; the tube width is 20 mm or less; the fluid channel height is 1.0 mm or less; the fluid channel width w 1  is 2.0 mm or less; the fluid diameter is 0.3 to 1.2 mm; and the thickness t of each wall is 0.4 mm or less. The ratio h 2 /t of the fin height h 2  to the wall thickness t satisfies the relation 0.5≦h 2 /t≦2.0. The ratio p 1 /w 1  of the fin pitch p 1  to the fluid channel width w 1  satisfies the relation 0.15≦p 1 /w 1 ≦1/n (where n is the number of the inner fins formed on one of the two surfaces).

BACKGROUND OF THE INVENTION

The present invention relates to a flat heat transfer tube, and more particularly to a flat heat transfer tube for use as a heat exchange tube of a heat exchanger, such as a condenser or an evaporator of a car air conditioner, an automotive radiator, or an automotive oil cooler.

Herein, the term “aluminum” encompasses aluminum alloys in addition to pure aluminum.

In recent years, a so-called multiflow condenser has been widely used as, for example, a condenser for use in a car air conditioner using a chlorofluorocarbon-based refrigerant, since the multiflow condenser can implement high performance, low pressure loss, and ultracompactness. As shown in FIG. 14, the multiflow condenser includes a first header 60 and a second header 61 arranged in parallel with and apart from each other; a plurality of flat heat exchange tubes 62 of aluminum arranged in parallel and having opposite ends connected to the respective first and second headers 60 and 61; corrugate fins 63 of aluminum, each being arranged in an air-passing clearance between adjacent heat exchange tubes 62 and brazed to the two heat exchange tubes 62; an inlet member 64 connected to an upper end portion of a circumferential wall of the first header 60; an outlet member 65 connected to a lower end portion of a circumferential wall of the second header 61; a first partition plate 66 provided in the interior of the first header 60 above a vertically intermediate position; and a second partition plate 67 provided in the interior of the second header 61 below a vertically intermediate position. The heat exchange tubes 62 arranged above the first partition plate 66, the heat exchange tubes 62 arranged between the first partition plate 66 and the second partition plate 67, and the heat exchange tubes 62 arranged below the second partition plate 67 sequentially reduce in number and constitute respective passes. In the condenser, a gas-phase refrigerant having flowed into the condenser through the inlet member 64 flows through the passes in a serpentine fashion until the refrigerant flows out of the outlet member 65 in a liquid phase.

The heat exchange tube 62 of the above-mentioned condenser is required to have not only an excellent heat exchange efficiency but also a resistance to pressure, since a high-pressure gas refrigerant is introduced thereinto.

A flat heat transfer tube for use as the heat exchange tube 62 of the above-mentioned condenser is disclosed in, for example, Japanese Patent Application Laid-Open (kokai) No. 6-185885. The flat heat transfer tube described in the publication is an aluminum extrudate; assumes a flat form having a pair of flat walls facing each other; and has a plurality of fluid channels arranged along the width of the flat heat transfer tube. A plurality of inner fins, each assuming the form of an elongated projection extending along the length of the flat heat transfer tube, are formed on each of two surfaces of the respective flat walls, the two surfaces facing each of the fluid channels. The height of the flat heat transfer tube is 2.0 mm or less; the height of the fluid channel is 1.2 mm or less; the ratio of the width of the fluid channel to the height of the fluid channel is to 6.0; the ratio of the height of the inner fin to the height of the fluid channel is 0.055 to 0.25; and the inner-fin pitch is 0.25 mm to 0.6 mm.

Table 1 shows the flat heat transfer tubes described as examples in the above-mentioned publication.

TABLE 1 RATIO RATIO OF THE OF THE INNER HEIGHT FIN WIDTH OF OF THE PITCH THE FLUID FLUID INNER TO THE CHANNEL HEIGHT HEIGHT DIAMETER FIN WIDTH OPPO- OF THE OF THE INNER OPPO- TO THE OF THE TUBE TUBE THICK- SITE FLUID INNER FIN SITE THICK- FLUID WIDTH HEIGHT NESS CENTER ENDS CHANNEL FIN PITCH CENTER ENDS NESS CHANNEL 1 17 mm 1.8 mm 0.45 mm 3.87 mm 3.755 mm 0.9 mm 0.15 mm 0.48 mm 1.06 mm 1.14 mm 0.33 0.12 2 ″ ″ ″ ″ ″ ″ ″ 1.03 mm 1.21 mm 1.21 mm ″ 0.27 3 ″ ″ ″ ″ ″ ″ ″ 1.24 mm 1.24 mm ″ ″ 4 ″ ″ ″ ″ ″ ″ ″ ″ 1.28 mm 1.28 mm ″ ″ 5 ″ ″ ″ ″ ″ ″ ″ ″ 1.33 mm 1.33 mm ″ ″ 6 ″ ″ ″ 1.81 mm 1.81 mm ″ ″ — 1.07 mm 1.07 mm ″ —

In the flat heat transfer tube No. 6 in Table 1, a single inner fin in the form of an elongated projection extending along the length of the flat heat transfer tube is formed on each of two surfaces of the respective flat walls, the two surfaces facing each of the fluid channels.

Recently, further improvement of heat exchange performance is required of the above-mentioned condenser. However, referring to Table 1 showing the flat heat transfer tubes described in the above-mentioned publication, there exists no flat heat transfer tube in which all of the tube width, the tube height, the thickness of the flat wall, the width of the fluid channel, the height of the fluid channel, the height of the inner fin, the inner-fin pitch, the fluid diameter, the ratio of the height of the inner fin to the thickness of the flat wall, and the ratio of the inner-fin pitch to the width of the fluid channel fall within respective optimum ranges. Particularly, since the thickness of the flat wall is large, and the ratio of the height of the inner fin to the thickness of the flat wall is low, heat transfer performance is insufficient. Therefore, the required further improvement of heat exchange performance of the condenser cannot be implemented.

SUMMARY OF THE INVENTION

An object of the present invention is to solve the above-mentioned problem and to provide a flat heat transfer tube capable of improving heat exchange performance of a heat exchanger.

To fulfill the above object, the present invention comprises the following modes.

1) A flat heat transfer tube which assumes a flat form having a pair of flat walls facing each other and has a plurality of fluid channels arranged along the width of the flat heat transfer tube; in which an inner fin in the form of an elongated projection extending along the length of the flat heat transfer tube is formed on each of two surfaces of the respective flat walls, the two surfaces facing each of the fluid channels; and which has a tube height H of 1.8 mm or less, a tube width W of 20 mm or less, a height h1 of the fluid channel of 1.0 mm or less, a width w1 of the fluid channel of 2.0 mm or less, and a fluid diameter Dh of 0.3 mm to 1.2 mm;

wherein a thickness t of each of the flat walls is 0.4 mm or less; two to five inner fins are formed on at least one of the two surfaces of the respective flat walls, the two surfaces facing at least one fluid channel; a ratio h2/t or h2 a/t, which is the ratio of a height h2 or h2 a of the inner fin to the thickness t of the flat wall, satisfies a relation 0.5≦h2/t≦2.0 or 0.5≦h2 a/t≦2.0, respectively; and a ratio p1/w1, p2/w1, or p3/w1, which is the ratio of a fin pitch p1, p2, or p3 of the plurality of inner fins to the width w1 of the fluid channel, satisfies a relation 0.15≦p1/w1≦1/n, 0.15≦p2/w1≦1/n, or 0.15≦p3/w1≦1/n, respectively (where n is the number of the inner fins formed on at least one of the two surfaces of the respective flat walls).

2) A flat heat transfer tube according to par. 1), wherein a plurality of the inner fins are formed on each of the two surfaces of the respective flat walls, the two surfaces facing each of the fluid channels, and the number of the inner fins is the same between the two surfaces.

3) A flat heat transfer tube according to par. 2), wherein the ratio of the height h2 or h2 a of the inner fin to the height h1 of the fluid channel satisfies a relation h2/h1<0.5 or h2 a/h1<0.5, respectively, and the positions of the inner fins along the width of each of the fluid channels are the same between the two surfaces of the respective flat walls.

4) A flat heat transfer tube according to par. 2), wherein the ratio of the height h2 or h2 a of the inner fin to the height h1 of the fluid channel satisfies a relation h2/h1≧0.5 or h2 a/h1 0.5, respectively, and the positions of the inner fins along the width of each of the fluid channels differ between the two surfaces of the respective flat walls.

5) A flat heat transfer tube according to par. 1), wherein a plurality of the inner fins are formed on each of the two surfaces of the respective flat walls, the two surfaces facing each of the fluid channels, and the number of the inner fins differs between the two surfaces.

6) A flat heat transfer tube according to par. 5), wherein the positions of the inner fins along the width of each of the fluid channels differ between the two surfaces of the respective flat walls.

7) A flat heat transfer tube according to par. 2), wherein the height h2 a of at least one of the inner fins formed on at least one of the two surfaces of the respective flat walls, the two surfaces facing each of the fluid channels, differs from the height h2 of the remaining inner fins.

8) A flat heat transfer tube which assumes a flat form having a pair of flat walls facing each other and has a plurality of fluid channels arranged along the width of the flat heat transfer tube; in which an inner fin in the form of an elongated projection extending along the length of the flat heat transfer tube is formed on each of two surfaces of the respective flat walls, the two surfaces facing each of the fluid channels; and which has a tube height H of 1.8 mm or less, a tube width W of 20 mm or less, a height h1 of the fluid channel of 1.0 mm or less, a width w1 of the fluid channel of 2.0 mm or less, and a fluid diameter Dh of 0.3 mm to 1.2 mm;

wherein a thickness t of each of the flat walls is 0.4 mm or less; a single inner fin is formed on at least one of the two surfaces of the respective flat walls, the two surfaces facing at least one fluid channel; a ratio h2/t, which is the ratio of a height h2 of the inner fin to the thickness t of the flat wall, satisfies a relation 0.5≦h2/t≦2.0; and a ratio w2 c/w1, which is the ratio of a distance w2 c between the single inner fin and a side surface of the fluid channel to the width w1 of the fluid channel, satisfies a relation 1/4≦w2 c/w1≦1/2.

9) A flat heat transfer tube according to par. 8), wherein a single inner fin is formed on each of the two surfaces of the respective flat walls, the two surfaces facing each of the fluid channels; the ratio of the height h2 of the inner fin to the height h1 of the fluid channel satisfies a relation h2/h1<0.5; and the position of the inner fin along the width of each of the fluid channels is the same between the two surfaces of the respective flat walls.

10) A flat heat transfer tube according to par. 8), wherein a single inner fin is formed on each of the two surfaces of the respective flat walls, the two surfaces facing each of the fluid channels; the ratio of the height h2 of the inner fin to the height h1 of the fluid channel satisfies a relation h2/h1≧0.5; and the position of the inner fin along the width of each of the fluid channels differs between the two surfaces of the respective flat walls.

11) A heat exchanger including a pair of header tanks arranged apart from each other; a plurality of flat heat exchange tubes extending between the two header tanks, arranged at predetermined intervals along the length of the header tanks, and having opposite end portions brazed to the header tanks after being inserted into respective tube insertion holes formed in the header tanks; and corrugate fins each disposed between and brazed to the adjacent heat exchange tubes;

wherein each of the heat exchange tubes is the flat heat transfer tube according to any one of pars. 1) to 10).

In the flat heat transfer tube of par. 1) or 8), the term “fluid diameter” means an equivalent diameter of a circular tube on the assumption that the heat transfer tube having a plurality of fluid channels each having a noncircular cross section is the circular tube having a single passage, and is defined by the following expression.

Dh=4Ac/L, where Ac is the total cross-sectional area of fluid channels, and L is the total wetted perimeter (total wetted side length) of fluid channels.

According to the flat heat transfer tube of any one of pars. 1) to 10), the tube width, the tube height, the thickness of the flat wall, the width of the fluid channel, the height of the fluid channel, the height of the inner fin, the fin pitch of the inner fins, the fluid diameter, the ratio of the height of the inner fin to the thickness of the flat wall, and the ratio of the fin pitch to the width of the fluid channel fall within respective optimum ranges. Therefore, the flat heat transfer tube exhibits excellent heat transfer performance. Accordingly, through use of the flat heat transfer tubes, a heat exchanger can further improve heat exchange performance.

According to the flat heat transfer tube of any one of pars. 5) to 10), an increase in pressure drop can be restrained.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view showing a flat heat transfer tube according to Embodiment 1 of the present invention;

FIG. 2 is a fragmentary enlarged view showing a single fluid channel of the flat heat transfer tube of FIG. 1;

FIG. 3 is a front view showing a sheet-like member from which the flat heat transfer tube of FIG. 1 is manufactured;

FIG. 4 is a front view showing a step in the course of manufacture of the flat heat transfer tube of FIG. 1 from the sheet-like member of FIG. 3;

FIG. 5 is a cross-sectional view showing a flat heat transfer tube according to Embodiment 2 of the present invention;

FIG. 6 is a fragmentary enlarged view showing a single fluid channel of the flat heat transfer tube of FIG. 5;

FIG. 7 is a fragmentary enlarged view showing a single fluid channel of a flat heat transfer tube according to Embodiment 3 of the present invention;

FIG. 8 is a fragmentary enlarged view showing a single fluid channel of a flat heat transfer tube according to Embodiment 4 of the present invention;

FIG. 9 is a fragmentary enlarged view showing a single fluid channel of a flat heat transfer tube according to Embodiment 5 of the present invention;

FIG. 10 is a fragmentary enlarged view showing a single fluid channel of a flat heat transfer tube according to Embodiment 6 of the present invention;

FIG. 11 is a fragmentary enlarged view showing a single fluid channel of a flat heat transfer tube according to Embodiment 7 of the present invention;

FIG. 12 is a graph showing the results of Evaluation Test 1 for Examples 1 to 3 and Comparative Examples 1 and 2;

FIG. 13 is a graph showing the results of Evaluation Test 1 for Examples 4 to 10 and Comparative Example 3; and

FIG. 14 is a perspective view showing a condenser for use in a car air conditioner.

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiments of the present invention will next be described with reference to the drawings. In the following description, the upper, lower, left-hand, and right-hand sides of FIGS. 1 to 11 will be referred to as “upper,” “lower,” “left,” and “right,” respectively.

In the drawings, like sections or components throughout the several views are denoted by like reference numerals, and repeated description thereof is omitted.

EMBODIMENT 1

The present embodiment is shown in FIGS. 1 to 4.

FIG. 1 shows the overall configuration of a flat heat transfer tube according to Embodiment 1 of the present invention. FIG. 2 shows, on an enlarged scale, a single fluid channel of the flat heat transfer tube according to Embodiment 1 of the present invention. FIG. 3 shows a sheet-like member from which the flat heat transfer tube is manufactured. FIG. 4 shows a step in the course of manufacture of the flat heat transfer tube from the sheet-like member.

In FIGS. 1 and 2, a flat heat transfer tube 1 is made of aluminum and includes flat upper and lower walls 2 and 3 (a pair of flat walls) facing each other; left and right side walls 4 and 5 extending between the left ends of the upper and lower walls 2 and 3 and between the right ends of the upper and lower walls 2 and 3, respectively; and a plurality of reinforcement walls 6 arranged at predetermined intervals between the left and right side walls 4 and 5 and extending between the upper and lower walls 2 and 3 and along the length of the flat heat transfer tube 1. Accordingly, the flat heat transfer tube 1 has a plurality of fluid channels 7 arranged therein along its width. Although unillustrated, a plurality of communication holes for establishing communication between the adjacent fluid channels 7 are formed in all of the reinforcement walls 6 in a staggered arrangement as viewed in plane.

Two to five; herein, three, inner fins 8, each assuming an elongated projection extending along the length of the flat heat transfer tube 1, are formed on surfaces 2 a and 3 a of the upper and lower walls 2 and 3, the surfaces 2 a and 3 a facing each of the fluid channels 7; i.e., are disposed on the upper and lower surfaces of each of the fluid channels 7. The number of the inner fins 8 is the same between the two surfaces 2 a and 3 a. All of the inner fins 8 have the same height. Further, the inner fins 8 formed on the surface 2 a of the upper wall 2 and the inner fins 8 formed on the surface 3 a of the lower wall 3 are located at the same positions along the width of the flat heat transfer tube 1.

The left side wall 4 is formed such that a side-wall-forming elongated projection 9 and a side-wall-forming elongated projection 11 are butt-brazed together. The side-wall-forming elongated projection 9 is formed integrally with a left end of the upper wall 2 in a downwardly projecting condition. The side-wall-forming elongated projection 11 is formed integrally with a left end of the lower wall 3 in an upwardly projecting condition. The right side wall 5 is formed integrally with the upper and lower walls 2 and 3.

The reinforcement walls 6 are formed such that reinforcement-wall-forming elongated projections 12 and 13 are butt-brazed to reinforcement-wall-forming elongated projections 15 and 14, respectively. The reinforcement-wall-forming elongated projections 12 and 13 are formed integrally with the upper wall 2 in a downwardly projecting condition. The reinforcement-wall-forming elongated projections 14 and 15 are formed integrally with the lower wall 3 in an upwardly projecting condition. Two kinds of the reinforcement-wall-forming elongated projections 12 and 13 having different thicknesses are formed on the upper wall 2 in such a manner as to alternate with each other along the left-right direction. Two kinds of the reinforcement-wall-forming elongated projections 14 and 15 having different thicknesses are formed on the lower wall 3 in such a manner as to alternate with each other along the left-right direction. The thick reinforcement-wall-forming elongated projections 12 integral with the upper wall 2 are brazed to the respective thin reinforcement-wall-forming elongated projections 15 integral with the lower wall 3. The thin reinforcement-wall-forming elongated projections 13 integral with the upper wall 2 are brazed to the respective thick reinforcement-wall-forming elongated projections 14 integral with the lower wall 3. Hereinafter, the thick reinforcement-wall-forming elongated projections 12 and 14 of the upper and lower walls 2 and 3, respectively, are referred to as the first reinforcement-wall-forming elongated projections. Similarly, the thin reinforcement-wall-forming elongated projections 13 and 15 of the upper and lower walls 2 and 3, respectively, are referred to as the second reinforcement-wall-forming elongated projections. The first reinforcement-wall-forming elongated projections 12 and 14 of the upper and lower walls 2 and 3 have grooves 16 and 17, respectively, formed on their distal end faces along their entire lengths. Distal end portions of the second reinforcement-wall-forming elongated projections 15 and 13 of the lower and upper walls 3 and 2 are fitted into the grooves 16 and 17 of the respective first reinforcement-wall-forming elongated projections 12 and 14 of the upper and lower walls 2 and 3, respectively. While distal end portions of the second reinforcement-wall-forming elongated projections 15 of the lower wall 3 are press-fitted into the grooves 16 of the respective first reinforcement-wall-forming elongated projections 12 of the upper wall 2, and distal end portions of the second reinforcement-wall-forming elongated projections 13 of the upper wall 2 are press-fitted into the grooves 17 of the respective first reinforcement-wall-forming elongated projections 14 of the lower wall 3, the reinforcement-wall-forming elongated projections 12 and 15 are brazed together, and the reinforcement-wall-forming elongated projections 13 and 14 are brazed together.

The tube height H of the heat transfer tube 1 is 1.8 mm or less; the tube width W of the heat transfer tube 1 is 20 mm or less; the height h1 of the fluid channel 7 is 1.0 mm or less; the width w1 of the fluid channel 7 (the distance between the opposite side surfaces of a single fluid channel 7; i.e., the distance between the surfaces of the second reinforcement-wall-forming elongated projections 13 and 15 of the two reinforcement walls 6 located on the opposite sides of the fluid channel 7, the surfaces facing the fluid channel 7) is 2.0 mm or less; the fluid diameter Dh is 0.3 mm to 1.2 mm; and the thickness t of each of the upper and lower walls 2 and 3 is 0.4 mm or less. The ratio of the height h2 of the inner fin 8 to the thickness t of each of the upper and lower walls 2 and 3; i.e., the ratio h2/t, satisfies the relation 0.5≦h2/t≦2.0. The ratio of the fin pitch (the distance between the thicknesswise centers of the inner fins 8) p1 of a plurality of the inner fins 8 to the width w1 of the fluid channel 7; i.e., the ratio p1/w1, satisfies the relation 0.15≦p1/w1≦1/n (n is the number of the inner fins 8 formed on each of the two surfaces 2 a and 3 a of the upper and lower walls 2 and 3). When the tube height H, the tube width W, the height h1 of the fluid channel 7, the width w1 of the fluid channel 7, the fluid diameter Dh, the thickness t of each of the upper and lower walls 2 and 3, the ratio of the height h2 of the inner fin 8 to the thickness t of each of the upper and lower walls 2 and 3; i.e., the ratio h2/t, and the ratio of the fin pitch p1 of the plurality of the inner fins 8 to the width w1 of the fluid channel 7; i.e., the ratio p1/w1, satisfy the above-mentioned respective requirements, the heat transfer performance of the flat heat transfer tube 1 is improved while an increase in pressure loss is restrained. Particularly, when the number of the inner fins 8 exceeds five or when the ratio of the height h2 of the inner fin 8 to the width t of each of the upper and lower walls 2 and 3; i.e., the ratio h2/t, exceeds 2.0, pressure loss increases greatly.

The inner fins 8 formed on the surface 2 a of the upper wall 2, the surface 2 a facing each of the fluid channels 7, and the inner fins 8 formed on the surface 3 a of the lower wall 3, the surface 3 a facing each of the fluid channels 7, are located at the same positions along the width of the flat heat transfer tube 1. Thus, in order to prevent the distal ends of the upper and lower inner fins 8 from butting against each other, the ratio of the height h2 of the inner fin 8 to the height h1 of the fluid channel 7; i.e., the ratio h2/h1, satisfies the relation h2/h1<0.5.

As shown in FIGS. 1 and 2, when the number of the inner fins 8 formed on each of the surfaces 2 a and 3 a of the upper and lower walls 2 and 3, the surfaces 2 a and 3 a facing each of the fluid channels 7, is three, preferably, the ratio w2/w1 is 1/12 to 7/20 inclusive, where w1 is the width of the fluid channel 7, and w2 is the distance between the thickness wise center of the left- or right-end inner fin 8 and the surface of the second reinforcement-wall-forming elongated projection 15 or 13 of the left- or right-hand reinforcement wall 6, the surface facing the fluid channel 7. In the case where four inner fins 8 are formed on each of the surfaces 2 a and 3 a of the upper and lower walls 2 and 3, the surfaces 2 a and 3 a facing each of the fluid channels 7, the ratio w2/w1 is preferably 1/16 to 11/40 inclusive. In the case where five inner fins 8 are formed, the ratio w2/w1 is preferably 1/20 to 1/5 inclusive.

The flat heat transfer tube 1 is manufactured from a heat-transfer-tube-forming sheet-like member 20 shown in FIG. 3.

In FIG. 3, the heat-transfer-tube-forming sheet-like member 20 is formed, by rolling, from a blank aluminum brazing sheet having a brazing material layer on each of opposite sides thereof. The heat-transfer-tube-forming sheet-like member 20 includes a flat upper-wall-forming portion 21 and a flat lower-wall-forming portion 22 having the same width and the same thickness and adapted to form the upper and lower walls 2 and 3, respectively; a connection portion 23 being slightly thicker than the upper- and lower-wall-forming portions 21 and 22, integrally connecting the upper- and lower-wall-forming portions 21 and 22, and adapted to form the right side wall 5; the side-wall-forming elongated projections 9 and 11, which are formed integrally with the side ends of the upper- and lower-wall-forming portions 21 and 22 opposite the connection portion 23, in an upwardly projecting condition and which are adapted to form the left side wall 4; a plurality of first and second reinforcement-wall-forming elongated projections 12, 13, 14, and 15, which are formed integrally with the upper- and lower-wall-forming portions 21 and 22 in an upwardly projecting condition and which are arranged at predetermined intervals in the left-right direction; and the inner fins 8, which are formed integrally with the upper- and lower-wall-forming portions 21 and 22 in an upwardly projecting condition in regions between the adjacent reinforcement-wall-forming elongated projections 12, 13, 14, and 15. The side-wall-forming elongated projections 9 and 11 are located symmetrically with respect to the centerline of the left-right direction of the connection portion 23; the first reinforcement-wall-forming elongated projections 12 of the upper-wall-forming portion 21 and the second reinforcement-wall-forming elongated projections 15 of the lower-wall-forming portion 22 are located symmetrically with respect to the centerline; the first reinforcement-wall-forming elongated projections 14 of the lower-wall-forming portion 22 and the second reinforcement-wall-forming elongated projections 13 of the upper-wall-forming portion 21 are located symmetrically with respect to the centerline; and the inner fins 8 of the upper-wall-forming portion 21 and the inner fins 8 of the lower-wall-forming portion 22 are located symmetrically with respect to the centerline.

The groove 16 is formed on the distal end face of each of the first reinforcement-wall-forming elongated projections 12 of the upper-wall-forming portion 21. The second reinforcement-wall-forming elongated projections 15 of the lower-wall-forming portion 22 are press-fitted into the respective grooves 16. The groove 17 is formed on the distal end face of each of the first reinforcement-wall-forming elongated projections 14 of the lower-wall-forming portion 22. The second reinforcement-wall-forming elongated projections 13 of the upper-wall-forming portion 21 are press-fitted into the respective grooves 17. The side-wall-forming elongated projections 9 and 11 of the upper- and lower-wall-forming portions 21 and 22 have the same dimensions; specifically, the same height and the same thickness. The first reinforcement-wall-forming elongated projections 12 of the upper-wall-forming portion 21 and the first reinforcement-wall-forming elongated projections 14 of the lower-wall-forming portion 22 have the same dimensions; specifically, the same height, the same thickness, the same width of the grooves 16 and 17, and the same depth of the grooves 16 and 17. Further, the second reinforcement-wall-forming elongated projections 13 of the upper-wall-forming portion 21 and the second reinforcement-wall-forming elongated projections 15 of the lower-wall-forming portion 22 have the same dimensions; specifically, the same height and the same thickness.

Next, the method of manufacturing the flat heat transfer tube 1 from the heat-transfer-tube-forming sheet-like member 20 will be described with reference to FIG. 4.

The heat-transfer-tube-forming sheet-like member 20 is gradually folded at the left and right sides of the connection portion 23 by a roll forming process (see FIG. 4( a)) until a hairpin shape is formed in the following conditions. The distal end faces of the two side-wall-forming elongated projections 9 and 11 butt against each other. The distal end portions of the second reinforcement-wall-forming elongated projections 13 and 15 are press-fitted into the grooves 17 and 16 of the first reinforcement-wall-forming elongated projections 14 and 12, respectively. A folded member 20A (see FIG. 4( b)) thus is yielded.

Subsequently, the folded member 20A is heated at a predetermined temperature for carrying out the following brazing through utilization of the above-mentioned brazing material layers: brazing together distal end portions of the two side-wall-forming elongated projections 9 and 11 so as to form the left side wall 4, brazing together distal end portions of the first and second reinforcement-wall-forming elongated projections 12 and 15 so as to form the reinforcement walls 6, and brazing together distal end portions of the first and second reinforcement-wall-forming elongated projections 14 and 13 so as to form the reinforcement walls 6. The connection portion 23 forms as the right side wall 5; the upper-wall-forming portion 21 forms the upper wall 2; and the lower-wall-forming portion 22 forms the lower wall 3. The flat heat transfer tube 1 thus is manufactured.

In the case where the flat heat transfer tubes 1 are used as, for example, heat exchange tubes 62 of a condenser shown in FIG. 14, the manufacture of the flat heat transfer tubes 1 may proceed simultaneously with the manufacture of the condenser. Specifically, the condenser is manufactured as follows. First, a plurality of the folded members 20A are prepared. Also are prepared a pair of aluminum headers 60 and 61 each having a plurality of folded-member insertion holes, and a plurality of aluminum corrugate fins 63. Then, the paired headers 60 and 61 are arranged apart from each other. The fins 63 and the same number of the folded members 20A as the number of the folded-member insertion holes are arranged in alternating layers such that opposite end portions of the folded members 20A are inserted into the respective folded-member insertion holes of the headers 60 and 61. Subsequently, the resultant assembly is heated at a predetermined temperature, whereby the flat heat transfer tubes 1 are manufactured as mentioned above, and, at the same time, the following brazing is simultaneously carried out through utilization of the brazing material layers of the heat-transfer-tube-forming sheet-like members 20: brazing together the flat heat transfer tubes 1 and the headers 60 and 61, and brazing together the flat heat transfer tubes 1 and the corrugate fins 63. The condenser thus is manufactured.

In the case where a refrigeration cycle using a chlorofluorocarbon-based refrigerant and having a compressor, a condenser, and an evaporator is used as a car air conditioner mounted on a vehicle; for example, an automobile, the heat exchanger provided with the above-mentioned flat heat transfer tubes 1 is used as the condenser of the refrigeration cycle. Also, the heat exchanger is used as the evaporator of the refrigeration cycle. Further, the heat exchanger may be mounted on an automobile as an oil cooler or a radiator provided with the above-mentioned flat heat transfer tubes 1.

In the case where a supercritical refrigeration cycle using a supercritical refrigerant, such as a CO₂ refrigerant, and having a compressor, a gas cooler, an evaporator, a pressure-reducing device, and an intermediate heat exchanger for performing heat exchange between the refrigerant flowing out from the gas cooler and the refrigerant flowing out from the evaporator is used as a car air conditioner mounted on a vehicle; for example, an automobile, the above-mentioned flat heat transfer tubes 1 may be used in the gas cooler or the evaporator.

In the above-described Embodiment 1, the inner fins 8 formed on a surface of the upper wall 2, the surface facing each of the fluid channels 7, and the inner fins 8 formed on a surface of the lower wall 3, the surface facing each of the fluid channels 7, are located at the same positions along the width of the flat heat transfer tube 1. However, the present invention is not limited thereto. The positions along the width of the flat heat transfer tube 1 may differ between the upper and lower walls 2 and 3. In this case, the ratio of the height h2 of the inner fin 8 to the height h1 of the fluid channel 7 may be higher than 0.5; i.e., h2/h1>0.5.

EMBODIMENT 2

The present embodiment is shown in FIGS. 5 and 6.

FIG. 5 shows the overall configuration of a flat heat transfer tube according to Embodiment 2 of the present invention. FIG. 6 shows, on an enlarged scale, a single fluid channel of the flat heat transfer tube according to Embodiment 2 of the present invention.

As shown in FIG. 5, two to five inner fins 8 and 26, each assuming an elongated projection extending along the length of a flat heat transfer tube 25, are formed on surfaces 2 a and 3 a of the upper and lower walls 2 and 3, the surfaces 2 a and 3 a facing each of the fluid channels 7; i.e., are disposed on the upper and lower surfaces of each of the fluid channels 7. The number of the inner fins 8 formed on one surface 2 a differs from the number of the inner fins 26 formed on the other surface 3 a. In FIG. 6, two inner fins 8 are formed on the surface 2 a of the upper wall 2, whereas three inner fins 26 are formed on the surface 3 a of the lower wall 3. The fluid channel 7 in which two inner fins 8 are formed on the surface 2 a of the upper wall 2 and the fluid channel 7 in which three inner fins 26 are formed on the surface 2 a of the upper wall 2 alternate along the width of the flat heat transfer tube 1. In the fluid channels 7, the height h2 a of each of the three inner fins 26 formed on one surface 2 a or 3 a is lower than the height h2 of the two inner fins 8 formed on the other surface 3 a or 2 a. Other configurational features of the flat heat transfer tube 25 is the same as those of the flat heat transfer tube 1 of Embodiment 1. The flat heat transfer tube 25 is manufactured in a manner similar to that of Embodiment 1. Also, in Embodiment 2, the tube height H of the heat transfer tube 25 is 1.8 mm or less; the tube width W of the heat transfer tube 25 is 20 mm or less; the height h1 of the fluid channel 7 is 1.0 mm or less; the width w1 of the fluid channel 7 is 2.0 mm or less; the fluid diameter Dh is 0.3 mm to 1.2 mm; and the thickness t of each of the upper and lower walls 2 and 3 is 0.4 mm or less. The ratio of the height h2 a of the inner fin 26 to the thickness t; i.e., the ratio h2 a/t satisfies the relation 0.5≦h2 a/t≦2.0, and the ratio of the height h2 of the inner fin 8 to the thickness t; i.e., the ratio h2/t, satisfies the relation 0.5≦h2/t≦2.0. Further, the ratio of the fin pitch p1 of the inner fins 26 to the width w1 of the fluid channel 7; i.e., the ratio p1/w1, satisfies the relation 0.15≦p1/w1≦1/n, and the ratio of the fin pitch p2 of the inner fins 8 to the width w1 of the fluid channel 7; i.e., the ratio p2/w1, satisfies the relation 0.15≦p2/w1≦1/n (n is the number of the inner fins 26 or 8 formed on each of the two surfaces 2 a and 3 a of the upper and lower walls 2 and 3). When the tube height H, the tube width W, the height h1 of the fluid channel 7, the width w1 of the fluid channel 7, the fluid diameter Dh, the thickness t of each of the upper and lower walls 2 and 3, the ratio of the height h2 a of the inner fin 26 to the thickness t; i.e., the ratio h2 a/t, the ratio of the height h2 of the inner fin 8 to the thickness t; i.e., the ratio h2/t, the ratio of the fin pitch p1 of the inner fins 26 to the width w1 of the fluid channel 7; i.e., the ratio p1/w1, and the ratio of the fin pitch p2 of the inner fins 8 to the width w1 of the fluid channel 7; i.e., the ratio p2/w1, satisfy the above-mentioned respective requirements, the heat transfer performance of the flat heat transfer tube 25 is improved while an increase in pressure loss is restrained.

Notably, the ratio of the height h2 or h2 a of the inner fin 8 or 26 to the height h1 of the fluid channel 7 may be less than 0.5 or greater than 0.5; i.e., (h2/h1 or h2 a/h1)<0.5 or (h2/h1 or h2 a/h1)>0.5.

When the number of the inner fins 8 formed on the surface 2 a of the upper wall 2 or on the surface 3 a of the lower wall 3, the surfaces 2 a and 3 a facing each of the fluid channels 7, is two, preferably, the ratio w2 a/w1 is 1/8 to 17/40 inclusive, where w1 is the width of the fluid channel 7, and w2 a is the distance between the thicknesswise center of the left- or right-hand inner fin 8 and the surface of the second reinforcement-wall-forming elongated projection 15 or 13 of the left- or right-hand reinforcement wall 6, the surface facing the fluid channel 7.

EMBODIMENT 3

The present embodiment is shown in FIG. 7.

FIG. 7 shows, on an enlarged scale, a single fluid channel of a flat heat transfer tube according to Embodiment 3 of the present invention.

As shown in FIG. 7, in each of the fluid channels 7 of the flat heat transfer tube 30, the height h2 of the three inner fins 8 formed on one surface 2 a or 3 a is equal to the height h2 of the two inner fins 8 formed on the other surface 3 a or 2 a.

Other configurational features of the flat heat transfer tube 30 is the same as those of the flat heat transfer tube of Embodiment 2. The flat heat transfer tube 30 is manufactured in a manner similar to that of Embodiment 2. Also, in Embodiment 3, the tube height H of the heat transfer tube 30 is 1.8 mm or less; the tube width W of the heat transfer tube 30 is 20 mm or less; the height h1 of the fluid channel 7 is 1.0 mm or less; the width w1 of the fluid channel 7 is 2.0 mm or less; the fluid diameter Dh is 0.3 mm to 1.2 mm; and the thickness t of each of the upper and lower walls 2 and 3 is 0.4 mm or less. The ratio of the height h2 of the inner fin 8 to the thickness t; i.e., the ratio h2/t, satisfies the relation 0.5≦h2/t≦2.0. Further, the ratio of the fin pitch p1 of the inner fins 8 to the width w1 of the fluid channel 7; i.e., the ratio p1/w1, satisfies the relation 0.15≦p1/w1≦1/n, and the ratio of the fin pitch p2 of the inner fins 8 to the width w1 of the fluid channel 7; i.e., the ratio p2/w1, satisfies the relation 0.15≦p2/w1≦1/n (n is the number of the inner fins 8 formed on each of the two surfaces 2 a and 3 a of the upper and lower walls 2 and 3). When the tube height H, the tube width W, the height h1 of the fluid channel 7, the width w1 of the fluid channel 7, the fluid diameter Dh, the thickness t of each of the upper and lower walls 2 and 3, the ratio of the height h2 of the inner fin 8 to the thickness t; i.e., the ratio h2/t, the ratio of the fin pitch p1 of the inner fins 8 to the width w1 of the fluid channel 7; i.e., the ratio p1/w1, and the ratio of the fin pitch p2 of the inner fins 8 to the width w1 of the fluid channel 7; i.e., the ratio p2/w1, satisfy the above-mentioned respective requirements, the heat transfer performance of the flat heat transfer tube 30 is improved while an increase in pressure loss is restrained.

Notably, the ratio of the height h2 of the inner fin 8 to the height h1 of the fluid channel 7 may be less than 0.5 or greater than 0.5; i.e., h2/h1≦0.5 or h2/h1>0.5.

EMBODIMENT 4

The present embodiment is shown in FIG. 8.

FIG. 8 shows, on an enlarged scale, a single fluid channel of a flat heat transfer tube according to Embodiment 4 of the present invention.

As shown in FIG. 8, in each of the fluid channels 7 of a flat heat transfer tube 35, the height of at least one of the three inner fins 8 and 26 formed on one surface 2 a or 3 a; herein, the height h2 a of the center inner fin 26, is lower than the height h2 of the remaining two inner fins 8. Also, the height h2 of the two inner fins 8 formed on the other surface 3 a or 2 a is equal to the height h2 of the opposite-side inner fins 8 of the three inner fins 8 and 26 formed on the one surface 2 a or 3 a.

Other configurational features of the flat heat transfer tube 35 is the same as those of the flat heat transfer tube of Embodiment 3. The flat heat transfer tube 35 is manufactured in a manner similar to that of Embodiment 3. Also, in Embodiment 4, the tube height H of the heat transfer tube 35 is 1.8 mm or less; the tube width W of the heat transfer tube 35 is 20 mm or less; the height h1 of the fluid channel 7 is 1.0 mm or less; the width w1 of the fluid channel 7 is 2.0 mm or less; the fluid diameter Dh is 0.3 mm to 1.2 mm; and the thickness t of each of the upper and lower walls 2 and 3 is 0.4 mm or less. The ratio of the height h2 of the inner fin 8 to the thickness t; i.e., the ratio h2/t, satisfies the relation 0.5≦h2/t≦2.0, and the ratio of the height h2 a of the inner fin 26 to the thickness t; i.e., the ratio h2 a/t satisfies the relation 0.5≦h2 a/t≦2.0. Further, the ratio of the fin pitch p1 of the inner fins 8 and 26 to the width w1 of the fluid channel 7; i.e., the ratio p1/w1, satisfies the relation 0.15≦p1/w1≦1/n, and the ratio of the fin pitch p2 of the inner fins 8 to the width w1 of the fluid channel 7; i.e., the ratio p2/w1, satisfies the relation 0.15≦p2/w1≦1/n (n is the number of the inner fins 26 or 8 formed on each of the two surfaces 2 a and 3 a of the upper and lower walls 2 and 3). When the tube height H, the tube width W, the height h1 of the fluid channel 7, the width w1 of the fluid channel 7, the fluid diameter Dh, the thickness t of each of the upper and lower walls 2 and 3, the ratio of the height h2 of the inner fin 8 to the thickness t; i.e., the ratio h2/t, the ratio of the height h2 a of the inner fin 26 to the thickness t; i.e., the ratio h2 a/t, the ratio of the fin pitch p1 of the inner fins 8 and 26 to the width w1 of the fluid channel 7; i.e., the ratio p1/w1, and the ratio of the fin pitch p2 of the inner fins 8 to the width w1 of the fluid channel 7; i.e., the ratio p2/w1, satisfy the above-mentioned respective requirements, the heat transfer performance of the flat heat transfer tube 35 is improved while an increase in pressure loss is restrained.

Notably, the ratio of the height h2 or h2 a of the inner fin 8 or 26 to the height h1 of the fluid channel 7 may be less than 0.5 or greater than 0.5; i.e., (h2/h1 or h2 a/h1)<0.5 or (h2/h1 or h2 a/h1)>0.5.

EMBODIMENT 5

The present embodiment is shown in FIG. 9.

FIG. 9 shows, on an enlarged scale, a single fluid channel of a flat heat transfer tube according to Embodiment 5 of the present invention.

As shown in FIG. 9, in each of the fluid channels 7 of a flat heat transfer tube 40, the height h2 a of the opposite-side inner fins 26 of the three inner fins 8 and 26 formed on one surface 2 a or 3 a is lower than the height h2 of the center inner fin 8. Also, the height h2 of the two inner fins 8 formed on the other surface 3 a or 2 a is equal to the height h2 of the center inner fin 8 of the three inner fins 8 and 26 formed on the one surface 2 a or 3 a.

Other configurational features of the flat heat transfer tube 40 is the same as those of the flat heat transfer tube of Embodiment 3. The flat heat transfer tube 40 is manufactured in a manner similar to that of Embodiment 3. Also, in Embodiment 5, the tube height H of the heat transfer tube 40 is 1.8 mm or less; the tube width W of the heat transfer tube 40 is 20 mm or less; the height h1 of the fluid channel 7 is 1.0 mm or less; the width w1 of the fluid channel 7 is 2.0 mm or less; the fluid diameter Dh is 0.3 mm to 1.2 mm; and the thickness t of each of the upper and lower walls 2 and 3 is 0.4 mm or less. The ratio of the height h2 of the inner fin 8 to the thickness t; i.e., the ratio h2/t, satisfies the relation 0.5≦h2/t≦2.0, and the ratio of the height h2 a of the inner fin 26 to the thickness t; i.e., the ratio h2 a/t satisfies the relation 0.5≦h2 a/t≦2.0. Further, the ratio of the fin pitch p1 of the inner fins 8 and 26 to the width w1 of the fluid channel 7; i.e., the ratio p1/w1, satisfies the relation 0.15≦p1/w1≦1/n, and the ratio of the fin pitch p2 of the inner fins 8 to the width w1 of the fluid channel 7; i.e., the ratio p2/w1, satisfies the relation 0.15≦p2/w1≦1/n (n is the number of the inner fins 26 or 8 formed on each of the two surfaces 2 a and 3 a of the upper and lower walls 2 and 3). When the tube height H, the tube width W, the height h1 of the fluid channel 7, the width w1 of the fluid channel 7, the fluid diameter Dh, the thickness t of each of the upper and lower walls 2 and 3, the ratio of the height h2 of the inner fin 8 to the thickness t; i.e., the ratio h2/t, the ratio of the height h2 a of the inner fin 26 to the thickness t; i.e., the ratio h2 a/t, the ratio of the fin pitch p1 of the inner fins 8 and 26 to the width w1 of the fluid channel 7; i.e., the ratio p1/w1, and the ratio of the fin pitch p2 of the inner fins 8 to the width w1 of the fluid channel 7; i.e., the ratio p2/w1, satisfy the above-mentioned respective requirements, the heat transfer performance of the flat heat transfer tube 40 is improved while an increase in pressure loss is restrained.

Notably, the ratio of the height h2 or h2 a of the inner fin 8 or 26 to the height h1 of the fluid channel 7 may be less than 0.5 or greater than 0.5; i.e., (h2/h1 or h2 a/h1)<0.5 or (h2/h1 or h2 a/h1)>0.5.

According to the heat transfer tubes of Embodiments 2 to 5 described above, the fluid channel 7 in which three inner fins 8 are formed on the surface 2 a of the upper wall 2 and the fluid channel 7 in which two inner fins 8 are formed on the surface 2 a of the upper wall 2 alternate along the width of the flat heat transfer tube 1, 25, 30, 35, or 40. Alternatively, all of the fluid channels 7 may be the same in the number of the inner fins 8 (e.g., three) formed on the surface 2 a of the upper wall 2 and the same in the number of the inner fins 8 and 26 (e.g., two) formed on the surface 3 a of the lower wall 3.

EMBODIMENT 6

The present embodiment is shown in FIG. 10.

FIG. 10 shows, on an enlarged scale, a single fluid channel of a flat heat transfer tube according to Embodiment 6 of the present invention.

As shown in FIG. 10, two inner fins 8, each assuming an elongated projection extending along the length of a flat heat transfer tube 45, are formed on the surfaces 2 a and 3 a of the upper and lower walls 2 and 3; i.e., are disposed on the upper and lower surfaces of each of the fluid channels 7. All of the inner fins 8 have the same height. The inner fins 8 formed on the surface 2 a of the upper wall 2 differ in position along the width of the flat heat transfer tube 45 from the inner fins 8 formed on the surface 3 a of the lower wall 3.

In FIG. 10, the distance between the right-hand inner fin 8 of the two inner fins 8 formed on the surface 2 a of the upper wall 2, and the surface of the second reinforcement-wall-forming elongated projection 13 of the right-hand reinforcement wall 6, the surface facing the fluid channel 7, is shorter than the distance between the left-hand inner fin 8 and the surface of the second reinforcement-wall-forming elongated projection 15 of the left-hand reinforcement wall 6, the surface facing the fluid channel 7. The distance between the left-hand inner fin 8 of the two inner fins 8 formed on the surface 3 a of the lower wall 3, and the surface of the second reinforcement-wall-forming elongated projection 15 of the left-hand reinforcement wall 6, the surface facing the fluid channel 7, is shorter than the distance between the right-hand inner fin 8 and the surface of the second reinforcement-wall-forming elongated projection 13 of the right-hand reinforcement wall 6, the surface facing the fluid channel 7. In this case, preferably, the ratio w2 b/w1 is 1/8 to 17/40 inclusive, where w1 is the width of the fluid channel 7, and w2 b is the distance between the thicknesswise center of one of the two inner fins 8, whichever closer to the second reinforcement-wall-forming elongated projection 13 or 15 of the reinforcement wall 6, formed on the upper or lower wall 2 or 3, and the surface of the second reinforcement-wall-forming elongated projection 13 or 15 of the reinforcement wall 6, the surface facing the closer inner fin 8 and the fluid channel 7.

Other configurational features of the flat heat transfer tube 25 is the same as those of the flat heat transfer tube 1 of Embodiment 1. The flat heat transfer tube 45 is manufactured in a manner similar to that of Embodiment 1. Also, in Embodiment 6, the tube height H of the heat transfer tube 45 is 1.8 mm or less; the tube width W of the heat transfer tube 45 is 20 mm or less; the height h1 of the fluid channel 7 is 1.0 mm or less; the width w1 of the fluid channel 7 is 2.0 mm or less; the fluid diameter Dh is 0.3 mm to 1.2 mm; and the thickness t of each of the upper and lower walls 2 and 3 is 0.4 mm or less. The ratio of the height h2 of the inner fin 8 to the thickness t of each of the upper and lower walls 2 and 3; i.e., the ratio h2/t, satisfies the relation 0.5≦h2/t≦2.0. Further, the ratio of the fin pitch p3 of the inner fins 8 to the width w1 of the fluid channel 7; i.e., the ratio p3/w1, satisfies the relation 0.15≦p3/w1≦1/2. When the tube height H, the tube width W, the height h1 of the fluid channel 7, the width w1 of the fluid channel 7, the fluid diameter Dh, the thickness t of each of the upper and lower walls 2 and 3, the ratio of the height h2 of the inner fin 8 to the thickness t of each of the upper and lower walls 2 and 3; i.e., the ratio h2/t, and the ratio of the fin pitch p3 of the inner fins 8 to the width w1 of the fluid channel 7; i.e., the ratio p3/w1, satisfy the above-mentioned respective requirements, the heat transfer performance of the flat heat transfer tube 45 is improved while an increase in pressure loss is restrained.

Notably, the ratio of the height h2 of the inner fin 8 to the height h1 of the fluid channel 7 may be less than 0.5 or greater than 0.5; i.e., h2/h1<0.5 or h2/h1>0.5.

In the flat heat transfer tube 45 of Embodiment 6 described above, the two inner fins 8 of the upper wall 2 and the two inner fins 8 of the lower wall 3 may be formed at the same positions along the width of the fluid channel 7. In this case, the ratio of the height h2 of the inner fin 8 to the height h1 of the fluid channel 7 is less than 0.5; i.e., h2/h1<0.5.

EMBODIMENT 7

The present embodiment is shown in FIG. 11.

As shown in FIG. 11, a single inner fin 8 assuming an elongated projection extending along the length of a flat heat transfer tube 50 is formed on surfaces 2 a and 3 a of the upper and lower walls 2 and 3, the surfaces 2 a and 3 a facing each of the fluid channels 7; i.e., is disposed on the upper and lower surfaces of each of the fluid channels 7. The inner fin 8 formed on the surface 2 a of the upper wall 2 differs in position along the width of the flat heat transfer tube 1 from the inner fin 8 formed on the surface 3 a of the lower wall 3.

In FIG. 11, the inner fin 8 formed on the surface 2 a of the upper wall 2 is offset rightward from the widthwise center of the fluid channel 7. In this case, the ratio of the distance w2 c between the thicknesswise center of the inner fin 8 and the surface of the second reinforcement-wall-forming elongated projection 13, which is formed on the upper wall 2, of the right-hand reinforcement wall 6, the surface facing the fluid channel 7, to the width w1 of the fluid channel 7; i.e., the ratio w2 c/w1, satisfies the relation 1/4≦w2 c/w1≦1/2. Also, the inner fin 8 formed on the surface 3 a of the lower wall 3 is offset leftward from the widthwise center of the fluid channel 7. In this case, the ratio of the distance w2 c between the thicknesswise center of the inner fin 8 and the surface of the second reinforcement-wall-forming elongated projection 15, which is formed on the lower wall 3, of the left-hand reinforcement wall 6, the surface facing the fluid channel 7, to the width w1 of the fluid channel 7; i.e., the ratio w2 c/w1, satisfies the relation 1/4≦w2 c/w1≦1/2.

Other configurational features of the flat heat transfer tube 50 is the same as those of the flat heat transfer tube 1 of Embodiment 1. The flat heat transfer tube 50 is manufactured in a manner similar to that of Embodiment 1. Also, in Embodiment 7, the tube height H of the heat transfer tube 50 is 1.8 mm or less; the tube width W of the heat transfer tube 50 is 20 mm or less; the height h1 of the fluid channel 7 is 1.0 mm or less; the width w1 of the fluid channel 7 is 2.0 mm or less; the fluid diameter Dh is 0.3 mm to 1.2 mm; and the thickness t of each of the upper and lower walls 2 and 3 is 0.4 mm or less. The ratio of the height h2 of the inner fin 8 to the thickness t of each of the upper and lower walls 2 and 3; i.e., the ratio h2/t, satisfies the relation 0.5≦h2/t≦2.0. When the tube height H, the tube width W, the height h1 of the fluid channel 7, the width w1 of the fluid channel 7, the fluid diameter Dh, the thickness t of each of the upper and lower walls 2 and 3, the ratio of the height h2 of the inner fin 8 to the thickness t of each of the upper and lower walls 2 and 3; i.e., the ratio h2/t, the ratio of the distance w2 c between the thicknesswise center of the inner fin 8 of the upper wall 2 and the surface of the second reinforcement-wall-forming elongated projection 13, which is formed on the upper wall 2, of the right-hand reinforcement wall 6, the surface facing the fluid channel 7, to the width w1 of the fluid channel 7; i.e., the ratio w2 c/w1, and the ratio of the distance w2 c between the thicknesswise center of the inner fin 8 of the lower wall 3 and the surface of the second reinforcement-wall-forming elongated projection 15, which is formed on the lower wall 3, of the left-hand reinforcement wall 6, the surface facing the fluid channel 7, to the width w1 of the fluid channel 7; i.e., the ratio w2 c/w1, satisfy the above-mentioned respective requirements, the heat transfer performance of the flat heat transfer tube 50 is improved while an increase in pressure loss is restrained.

Notably, the ratio of the height h2 of the inner fin 8 to the height h1 of the fluid channel 7 may be less than 0.5 or greater than 0.5; i.e., h2/h1<0.5 or h2/h1>0.5.

In the flat heat transfer tube 50 of Embodiment 7 described above, the inner fin 8 of the upper wall 2 and the inner fin 8 of the lower wall 3 may be formed at the same position along the width of the fluid channel 7. In this case, in order for the above-mentioned ratio w2 c/w1 to satisfy the relation 1/4≦w2 c/w1≦1/2, both of the inner fins 8 are formed at the widthwise center of the fluid channel 7. The ratio of the height h2 of the inner fin 8 to the height h1 of the fluid channel 7 is less than 0.5; i.e., h2/h1<0.5.

According to the flat heat transfer tubes 25, 30, 35, 40, 45, and 50 of Embodiments 2 to 7 described above, in each of the fluid channel 7, the distance between the distal end of one of a plurality of the inner fins 8 or 26 formed on one surface 2 a or 3 a and the distal end of an inner fin adjacent to the said inner fin and formed on the other surface 3 a or 2 a is greater than that in the flat heat transfer tube of Embodiment 1. Thus, an increase in pressure loss can be restrained.

The flat heat transfer tubes of Embodiments 1 to 7 described above are formed by subjecting the respective sheet-like members to folding and brazing. However, the flat heat transfer tube according to the present invention can also be applied to extrudates.

Next, specific examples of the flat heat transfer tube of the present invention will be described together with Comparative Examples.

EXAMPLES 1 TO 3

The flat heat transfer tubes of Examples 1 to 3 use the configuration of Embodiment 1 described above. Prepared were the flat heat transfer tubes each having a tube length of 100 mm, a tube height H of 1.20 mm, a tube width W of 16 mm, a thickness t of each of the upper and lower walls of 0.25 mm, a height h1 of the fluid channel of 0.7 mm, a width w1 of the fluid channel of 1.33 mm, a number n of the inner fins formed on a surface of each of the upper and lower walls, the surface facing each of the fluid channels, of 3, a fin pitch p1 of the inner fins of 0.25 mm, a fluid diameter Dh of 0.45 mm, and a height h2 of the inner fin of 0.2 mm (Example 1), 0.25 mm (Example 2), and 0.3 mm (Example 3). The ratio of the height h2 of the inner fin to the thickness t of each of the upper and lower walls; i.e., the ratio h2/t, is 0.8 for the flat heat transfer tube of Example 1, 1.0 for the flat heat transfer tube of Example 2, or 1.2 for the flat heat transfer tube of Example 3.

COMPARATIVE EXAMPLES 1 AND 2

The flat heat transfer tube of Comparative Example 1 was prepared under the same conditions as for Examples 1 to 3 except that the inner fins are not formed. The flat heat transfer tube of Comparative Example 2 was prepared under the same conditions as for Examples 1 to 3 except that the height h2 of the inner fin was 0.1 mm. The ratio of the height h2 of the inner fin to the thickness t of each of the upper and lower walls; i.e., the ratio h2/t, is 0 for the flat heat transfer tube of Comparative Example 1 and 0.4 for the flat heat transfer tube of Comparative Example 2.

EXAMPLES 4 TO 10

The flat heat transfer tubes of Examples 4 to 10 use the configuration of Embodiment 1 described above. Prepared were the flat heat transfer tubes each having a tube length of 100 mm, a tube height H of 1.20 mm, a tube width W of 16 mm, a thickness t of each of the upper and lower walls of 0.25 mm, a height h1 of the fluid channel of 0.7 mm, a width w1 of the fluid channel of 1.33 mm, a number n of the inner fins formed on a surface of each of the upper and lower walls, the surface facing each of the fluid channels, of 3, a height h2 of the inner fin of 0.25 mm, a fluid diameter Dh of 0.45 mm, and a fin pitch p1 of the inner fins of 0.20 mm (Example 4), 0.25 mm (Example 5), 0.30 mm (Example 6), 0.35 mm (Example 7), 0.40 mm (Example 8), 0.45 mm (Example 9), and 0.50 mm (Example 10). The ratio of the fin pitch p1 of a plurality of the inner fins to the width w1 of the fluid channel; i.e., the ratio p1/w1, is 0.1504 for the flat heat transfer tube of Example 4, 0.1880 for the flat heat transfer tube of Example 5, 0.2256 for the flat heat transfer tube of Example 6, 0.2632 for the flat heat transfer tube of Example 7, 0.300 for the flat heat transfer tube of Example 8, 0.3383 for the flat heat transfer tube of Example 9, and 0.3759 for the flat heat transfer tube of Example 10.

COMPARATIVE EXAMPLE 3

The flat heat transfer tube of Comparative Example 3 was prepared under the same conditions as for Examples 4 to 10 except that the fin pitch p1 of the inner fins was 0.16 mm. The ratio of the fin pitch p1 of a plurality of the inner fins to the width w1 of the fluid channel; i.e., the ratio p1/w1, is 0.12 for the flat heat transfer tube of Comparative Example 3.

Evaluation Test 1:

A refrigerant vapor (R134a) having a temperature of 60° C. was passed through the flat heat transfer tubes of Examples 1 to 10 and Comparative Examples 1 to 3; the temperature of an atmosphere around the flat heat transfer tubes was set to 27° C.; and while the refrigerant vapor and the atmosphere were maintained at the above-mentioned respective temperatures, the average overall heat transfer coefficient was measured. With the average overall heat transfer coefficient of the flat heat transfer tube of Comparative Example 1 taken as 1.00, an average-overall-heat-transfer-coefficient ratio was obtained for the remaining flat heat transfer tubes. FIG. 12 shows the test results of Examples 1 to 3 and Comparative Examples 1 and 2. FIG. 13 shows the test results of Examples 4 to 10 and Comparative Example 3.

As is apparent from FIG. 12, when the ratio of the height h2 of the inner fin to the thickness t of each of the upper and lower walls; i.e., the ratio h2/t, is 0.5 or higher, the average overall heat transfer coefficient markedly increases. As is apparent from FIG. 13, when the ratio of the fin pitch p1 of a plurality of the inner fins to the width w1 of the fluid channel; i.e., the ratio p1/w1, is 0.15 or higher, the average overall heat transfer coefficient markedly increases.

EXAMPLE 11

The flat heat transfer tube of Example 11 uses the configuration of Embodiment 3 described above. Prepared was the flat heat transfer tube having a tube length of 100 mm, a tube height H of 1.0 mm, a tube width W of 16 mm, a thickness t of each of the upper and lower walls of 0.2 mm, a height h1 of the fluid channel of 0.6 mm, a width w1 of the fluid channel of 1.33 mm, a number n of the inner fins formed on one of two surfaces of the upper and lower walls, the two surfaces facing each of the fluid channels, of 3, a number n of the inner fins formed on the other surface of the two surfaces of 2, a fin pitch p1 of the three inner fins formed on the one of the two surfaces of the upper and lower walls of 0.3 mm, a fin pitch p2 of the two inner fins formed on the other surface of the two surfaces of 0.35 mm, a distance w2 between the opposite-side inner fins of the three inner fins formed on the one of the two surfaces of the upper and lower walls, the two surfaces facing each of the fluid channels, and the second reinforcement-wall-forming elongated projections of the respective opposite-side reinforcement walls of 0.33 mm, a distance w2 a between the two inner fins formed on the other surface of the two surfaces of the upper and lower walls, the two surfaces facing each of the fluid channels, and the second reinforcement-wall-forming elongated projections of the respective opposite-side reinforcement walls of 0.49 mm, a fluid diameter Dh of 0.546 mm, and a height h2 of the inner fin of 0.25 mm. The ratio of the height h2 of the inner fin to the thickness t of each of the upper and lower walls; i.e., the ratio h2/t, is 1.25. The ratio of the fin pitch p1 of the three inner fins formed on the one surface of the two surfaces to the width w1 of the fluid channel; i.e., the ratio p1/w1, is 0.23. The ratio of the fin pitch p2 of the two inner fins formed on the other surface of the two surfaces to the width w1 of the fluid channel; i.e., the ratio p2/w1, is 0.26.

EXAMPLE 12

The flat heat transfer tube of Example 12 uses the configuration of Embodiment 4 described above. The flat heat transfer tube of Example 12 was prepared under the same conditions as for Example 11 except for the following: the fluid diameter Dh was 0.560 mm, and the height h2 a of the center inner fin of the three inner fins formed on one of two surfaces of the upper and lower walls, the two surfaces facing each of the fluid channels, was 0.2 mm. In the case of the inner fin having a height h2 of 0.25 mm, the ratio of the height h2 of the inner fin to the thickness t of each of the upper and lower walls; i.e., the ratio h2/t, is 1.25. In the case of the inner fin having a height h2 a of 0.2 mm, the ratio of the height h2 a of the inner fin to the thickness t of each of the upper and lower walls; i.e., the ratio h2 a/t, is 1.

EXAMPLE 13

The flat heat transfer tube of Example 13 uses the configuration of Embodiment 5 described above. The flat heat transfer tube of Example 13 was prepared under the same conditions as for Example 11 except for the following: the fluid diameter Dh was 0.576 mm, and the height h2 a of the opposite-side inner fins of the three inner fins formed on one of two surfaces of the upper and lower walls, the two surfaces facing each of the fluid channels, was 0.2 mm. In the case of the inner fin having a height h2 of 0.25 mm, the ratio of the height h2 of the inner fin to the thickness t of each of the upper and lower walls; i.e., the ratio h2/t, is 1.25. In the case of the inner fin having a height h2 a of 0.2 mm, the ratio of the height h2 a of the inner fin to the thickness t of each of the upper and lower walls; i.e., the ratio h2 a/t, is 1.

Evaluation Test 2:

By use of the flat heat transfer tubes of Examples 11 to 13, the average overall heat transfer coefficient was measured in a manner similar to that of Evaluation Test 1 described above. When the average overall heat transfer coefficient was measured, the differential pressure between the inlet and the outlet of each of the flat heat transfer tubes was also measured by use of a differential pressure gauge so as to determine a pressure loss for the flat heat transfer tubes.

Table 2 shows the average-overall-heat-transfer-coefficient ratios of the flat heat transfer tubes of Examples 11 to 13 which were obtained with the average overall heat transfer coefficient of the flat heat transfer tube of Comparative Example 1 taken as 1.00, and the pressure-loss ratios of Examples 12 and 13 which were obtained with the pressure loss of Example 11 taken as 1.00.

TABLE 2 AVERAGE OVERALL PRESSURE LOSS HEAT TRANSFER RATIO COEFFICIENT RATIO EXAMPLES 11 1.00 2.30 12 0.95 2.21 13 0.90 2.11

As is apparent from Table 2, the average overall heat transfer coefficients of the flat heat transfer tubes of Examples 11 to 13 are markedly increased as compared with the flat heat transfer tube in which no inner fins are formed. Also, as the distance between the distal ends of the laterally adjacent inner fins formed on the upper and lower walls, respectively, increases, the pressure loss lowers. 

1: A flat heat transfer tube which assumes a flat form having a pair of flat walls facing each other and has a plurality of fluid channels arranged along the width of the flat heat transfer tube; in which an inner fin in the form of an elongated projection extending along the length of the flat heat transfer tube is formed on each of two surfaces of the respective flat walls, the two surfaces facing each of the fluid channels; and which has a tube height H of 1.8 mm or less, a tube width W of 20 mm or less, a height h1 of the fluid channel of 1.0 mm or less, a width w1 of the fluid channel of 2.0 mm or less, and a fluid diameter Dh of 0.3 mm to 1.2 mm; wherein a thickness t of each of the flat walls is 0.4 mm or less; two to five inner fins are formed on at least one of the two surfaces of the respective flat walls, the two surfaces facing at least one fluid channel; a ratio h2/t or h2 a/t, which is the ratio of a height h2 or h2 a of the inner fin to the thickness t of the flat wall, satisfies a relation 0.5≦h2/t≦2.0 or 0.5≦h2 a/t≦2.0, respectively; and a ratio p1/w1, p2/w1, or p3/w1, which is the ratio of a fin pitch p1, p2, or p3 of the plurality of inner fins to the width w1 of the fluid channel, satisfies a relation 0.15≦p1/w1≦1/n, 0.15≦p2/w1≦1/n, or 0.15≦p3/w1≦1/n, respectively (where n is the number of the inner fins formed on at least one of the two surfaces of the respective flat walls). 2: A flat heat transfer tube according to claim 1, wherein a plurality of the inner fins are formed on each of the two surfaces of the respective flat walls, the two surfaces facing each of the fluid channels, and the number of the inner fins is the same between the two surfaces. 3: A flat heat transfer tube according to claim 2, wherein the ratio of the height h2 or h2 a of the inner fin to the height h1 of the fluid channel satisfies a relation h2/h1<0.5 or h2 a/h1<0.5, respectively, and the positions of the inner fins along the width of each of the fluid channels are the same between the two surfaces of the respective flat walls. 4: A flat heat transfer tube according to claim 2, wherein the ratio of the height h2 or h2 a of the inner fin to the height h1 of the fluid channel satisfies a relation h2/h1≧0.5 or h2 a/h1≧0.5, respectively, and the positions of the inner fins along the width of each of the fluid channels differ between the two surfaces of the respective flat walls. 5: A flat heat transfer tube according to claim 1, wherein a plurality of the inner fins are formed on each of the two surfaces of the respective flat walls, the two surfaces facing each of the fluid channels, and the number of the inner fins differs between the two surfaces. 6: A flat heat transfer tube according to claim 5, wherein the positions of the inner fins along the width of each of the fluid channels differ between the two surfaces of the respective flat walls. 7: A flat heat transfer tube according to claim 2, wherein the height h2 a of at least one of the inner fins formed on at least one of the two surfaces of the respective flat walls, the two surfaces facing each of the fluid channels, differs from the height h2 of the remaining inner fins. 8: A flat heat transfer tube which assumes a flat form having a pair of flat walls facing each other and has a plurality of fluid channels arranged along the width of the flat heat transfer tube; in which an inner fin in the form of an elongated projection extending along the length of the flat heat transfer tube is formed on each of two surfaces of the respective flat walls, the two surfaces facing each of the fluid channels; and which has a tube height H of 1.8 mm or less, a tube width W of 20 mm or less, a height h1 of the fluid channel of 1.0 mm or less, a width w1 of the fluid channel of 2.0 mm or less, and a fluid diameter Dh of 0.3 mm to 1.2 mm; wherein a thickness t of each of the flat walls is 0.4 mm or less; a single inner fin is formed on at least one of the two surfaces of the respective flat walls, the two surfaces facing at least one fluid channel; a ratio h2/t, which is the ratio of a height h2 of the inner fin to the thickness t of the flat wall, satisfies a relation 0.5≦h2/t≦2.0; and a ratio w2 c/w1, which is the ratio of a distance w2 c between the single inner fin and a side surface of the fluid channel to the width w1 of the fluid channel, satisfies a relation 1/4≦w2 c/w1≦1/2. 9: A flat heat transfer tube according to claim 8, wherein a single inner fin is formed on each of the two surfaces of the respective flat walls, the two surfaces facing each of the fluid channels; the ratio of the height h2 of the inner fin to the height h1 of the fluid channel satisfies a relation h2/h1<0.5; and the position of the inner fin along the width of each of the fluid channels is the same between the two surfaces of the respective flat walls. 10: A flat heat transfer tube according to claim 8, wherein a single inner fin is formed on each of the two surfaces of the respective flat walls, the two surfaces facing each of the fluid channels; the ratio of the height h2 of the inner fin to the height h1 of the fluid channel satisfies a relation h2/h1≧0.5; and the position of the inner fin along the width of each of the fluid channels differs between the two surfaces of the respective flat walls. 11: A heat exchanger including a pair of header tanks arranged apart from each other; a plurality of flat heat exchange tubes extending between the two header tanks, arranged at predetermined intervals along the length of the header tanks, and having opposite end portions brazed to the header tanks after being inserted into respective tube insertion holes formed in the header tanks; and corrugate fins each disposed between and brazed to the adjacent heat exchange tubes; wherein each of the heat exchange tubes is the flat heat transfer tube according to claim
 1. 12: A heat exchanger including a pair of header tanks arranged apart from each other; a plurality of flat heat exchange tubes extending between the two header tanks, arranged at predetermined intervals along the length of the header tanks, and having opposite end portions brazed to the header tanks after being inserted into respective tube insertion holes formed in the header tanks; and corrugate fins each disposed between and brazed to the adjacent heat exchange tubes; wherein each of the heat exchange tubes is the flat heat transfer tube according to claim
 2. 13: A heat exchanger including a pair of header tanks arranged apart from each other; a plurality of flat heat exchange tubes extending between the two header tanks, arranged at predetermined intervals along the length of the header tanks, and having opposite end portions brazed to the header tanks after being inserted into respective tube insertion holes formed in the header tanks; and corrugate fins each disposed between and brazed to the adjacent heat exchange tubes; wherein each of the heat exchange tubes is the flat heat transfer tube according to claim
 3. 14: A heat exchanger including a pair of header tanks arranged apart from each other; a plurality of flat heat exchange tubes extending between the two header tanks, arranged at predetermined intervals along the length of the header tanks, and having opposite end portions brazed to the header tanks after being inserted into respective tube insertion holes formed in the header tanks; and corrugate fins each disposed between and brazed to the adjacent heat exchange tubes; wherein each of the heat exchange tubes is the flat heat transfer tube according to claim
 4. 15: A heat exchanger including a pair of header tanks arranged apart from each other; a plurality of flat heat exchange tubes extending between the two header tanks, arranged at predetermined intervals along the length of the header tanks, and having opposite end portions brazed to the header tanks after being inserted into respective tube insertion holes formed in the header tanks; and corrugate fins each disposed between and brazed to the adjacent heat exchange tubes; wherein each of the heat exchange tubes is the flat heat transfer tube according to claim
 5. 16: A heat exchanger including a pair of header tanks arranged apart from each other; a plurality of flat heat exchange tubes extending between the two header tanks, arranged at predetermined intervals along the length of the header tanks, and having opposite end portions brazed to the header tanks after being inserted into respective tube insertion holes formed in the header tanks; and corrugate fins each disposed between and brazed to the adjacent heat exchange tubes; wherein each of the heat exchange tubes is the flat heat transfer tube according to claim
 6. 17: A heat exchanger including a pair of header tanks arranged apart from each other; a plurality of flat heat exchange tubes extending between the two header tanks, arranged at predetermined intervals along the length of the header tanks, and having opposite end portions brazed to the header tanks after being inserted into respective tube insertion holes formed in the header tanks; and corrugate fins each disposed between and brazed to the adjacent heat exchange tubes; wherein each of the heat exchange tubes is the flat heat transfer tube according to claim
 7. 18: A heat exchanger including a pair of header tanks arranged apart from each other; a plurality of flat heat exchange tubes extending between the two header tanks, arranged at predetermined intervals along the length of the header tanks, and having opposite end portions brazed to the header tanks after being inserted into respective tube insertion holes formed in the header tanks; and corrugate fins each disposed between and brazed to the adjacent heat exchange tubes; wherein each of the heat exchange tubes is the flat heat transfer tube according to claim
 8. 19: A heat exchanger including a pair of header tanks arranged apart from each other; a plurality of flat heat exchange tubes extending between the two header tanks, arranged at predetermined intervals along the length of the header tanks, and having opposite end portions brazed to the header tanks after being inserted into respective tube insertion holes formed in the header tanks; and corrugate fins each disposed between and brazed to the adjacent heat exchange tubes; wherein each of the heat exchange tubes is the flat heat transfer tube according to claim
 9. 20: A heat exchanger including a pair of header tanks arranged apart from each other; a plurality of flat heat exchange tubes extending between the two header tanks, arranged at predetermined intervals along the length of the header tanks, and having opposite end portions brazed to the header tanks after being inserted into respective tube insertion holes formed in the header tanks; and corrugate fins each disposed between and brazed to the adjacent heat exchange tubes; wherein each of the heat exchange tubes is the flat heat transfer tube according to claim
 10. 